Flywheel Sports has signed up a new, deep-pocketed investor — and she’s one tough trainer.

The Big Apple-based chain of indoor cycling studios is gearing up for a nationwide expansion with the backing of Jillian Michaels — the hard-charging fitness coach from the reality TV series “The Biggest Loser.”

Specific terms of the deal couldn’t be learned, but sources said Michaels will take a minority stake in Flywheel to help open upwards of a dozen new spinning studios by the end of next year.

Flywheel — whose regulars have included Ivanka Trump, Jimmy Fallon and Katie Couric — currently operates six spinning studios in New York City, the Hamptons and Boca Raton, Fla.

The chain will continue to be led by co-founders Jay Galluzzo and Ruth Zukerman as it works with Michaels to add new locations in Chicago, Atlanta, Millburn, NJ, and South Beach, Fla., this fall.

“This is not meant to be an endorsement,” Galluzzo told The Post, emphasizing that Michaels will not become the face of the chain. “You’re not going to see Jillian Michaels on Flywheel posters everywhere.”

Instead, Flywheel will tap Michaels’ experience as it scouts new studio sites across the US and overseas.

The deal with Michaels is the latest salvo in Flywheel’s grueling battle with crosstown rival SoulCycle. As first reported by The Post, SoulCycle was acquired this year by gym giant Equinox, which plans to expand.